The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Caster angle is one vehicle characteristic that can impact vehicle handling and ride comfort. Caster angle is generally defined by the angle, when viewed perpendicular to the side of the vehicle, between an axis perpendicular to the ground at the contact patch of a vehicle wheel and a real or virtual kingpin axis. When referring to a steerable wheel (e.g., front wheel of a front wheel steering vehicle), the kingpin axis is the axis about which the wheel rotates when steering. When referring to a non-steerable wheel (e.g., a rear wheel of a front wheel steering vehicle), the kingpin axis can generally be the axis about which the wheel would tend to rotate when a force is applied perpendicular to the side of to the wheel. In some vehicle suspensions, the virtual kingpin axis is the axis between two joints (e.g., ball joints) that connect to the wheel knuckle to two control arms. In some other vehicle suspensions, the virtual kingpin axis is determined based on the combined geometry of multiple control arms or other links between the knuckle and the vehicle's frame. In some other suspensions, the virtual kingpin axis is perpendicular to the ground surface and extends from the contact patch through the center of the wheel.
Certain dynamic conditions and compliance in the suspension can cause the caster angle of a vehicle's knuckle to change from the preferred caster angle. For example, hard breaking or acceleration can cause the knuckle to rotate generally about the wheel's rotational axis, which changes the angle of the virtual kingpin axis relative to the road surface. This change is typically referred to as caster windup. In some situations, such caster windup can negatively impact the vehicle performance. For example, caster windup could cause the wheel to contact the body, or some suspension components to bottom out. Caster windup can also result in a change of camber and toe angle of the vehicle wheel.
In some suspensions, caster windup is limited by a rigid member, typically referred to as an integral link. The integral link typically extends between a location on the knuckle and a location on one of the control arms (e.g., the lower control arm). The integral link acts in tension or compression (depending on the rotational direction of the caster windup) to prevent caster angle change. Since the integral link is a rigid body, caster windup is typically limited to any compliance that may exist in the connections (e.g., bushings) between the integral link and the knuckle or the control arm.
However, the integral link adds additional weight, cost, complexity, and packaging constraints on the suspension design. Additionally, in some situations, it may be advantageous to adjust or tune the amount of permitted caster windup during operation of the vehicle.
Accordingly, these issues with caster windup are addressed by the present disclosure.